A. Technical Field
The present invention relates to a cement additive, its production process and use. More specifically, it relates to a specific cement dispersant, its production process, a cement admixture in which an antifoaming agent is added to another cement dispersant and a cement composition, and these cement additives can give to a cement composition properties of achieving a high water reducing rate, preventing a reduction in the obtained flowability (called "slump loss") which occurs with the passage of time, and providing an appropriate stable amount of entrained air with the passage of time.
B. Background Art
The improvement of durability and strength of a concrete structure has been strongly desired in the concrete industry of nowadays and it is an important theme to reduce the amount of unit water. There are many proposals for polycarboxylic acid-based cement dispersants because they exhibit higher water reducing capability than conventional naphthalene-based cement dispersants. For instance, Japanese Patent Publication (Kokoku) No. Showa 58-38380 (JP-B-58038380)proposes a cement dispersant essentially containing a copolymer which comprises a polyethylene glycol monoallyl ether monomer, a maleic acid-based monomer and a monomer copolymerizable with these monomers in a specific ratio. However, the water reducing capability is not sufficient for cement compositions.